EMC is a service provider in the power transmission and distribution sector.
It was announced in June that EMC would make additional investment of up to Rs 100 crore as primary equity capital in McNally.
EMC, through its entity MKN Investments, already has 12.5 per cent shareholding in the company.
In a tweet, Competition Commission of India (CCI) said it has approved "acquisition of 19.77 per cent shareholding in McNally Bharat Engineering Company Ltd by EMC Ltd".
CCI keeps a tab on anti-competitive practices across sectors in the market place.
Besides, there would be an open offer by EMC and Williamson Magor Group for purchasing an additional 26 per cent stake.
McNally is an engineering firm that provides turnkey solutions in the areas of power, steel and aluminium, among others.